Historically, insurance coverage for drug, alcohol, and mental health (DAMH) care has been more limited than coverage for other forms of general health care. For decades, insurers defended this difference with arguments that equal coverage for DAMH care would lead to excessive use and high costs. More restrictive coverage has contributed over time to a large treatment gap in which most people in need of DAMH care have not received it. For those who have received care, financial protection has tended to be weaker. Since the 1990s, a series of state and federal laws have attempted to regulate insurance and mandate DAMH parity. One of the most comprehensive efforts has been the 2008 Paul Wellstone & Pete Domenici Mental Health Parity & Addiction Equity Act (MHPAEA). This federal law seeks to strengthen private insurance coverage for DAMH care, but its effectiveness to date remains largely unknown. The purpose of this project is: (1) to investigate the effects of MHPAEA on how people access and pay for DAMH care; and (2) to measure racial/ethnic disparities in access to DAMH care and assess how MHPAEA has affected them. Principles of health economics predict MHPAEA will improve financial protection for DAMH care recipients, reducing uncertainty about out-of-pocket expenses and limiting risk for high, potentially catastrophic costs. Another less probable outcome is that MHPAEA will increase DAMH treatment rates as better coverage makes care more affordable. According to the Institute of Medicine model of health care disparities, however, institutional factors and discrimination may intervene to perpetuate and potentially deepen racial/ethnic disparities in access to DAMH care despite the new protections afforded by MHPAEA. To research these issues, this study will employ a quasi-experimental design using secondary analysis of existing data. Difference-in-differences models will be fit with pooled independent cross sections of survey data from the National Survey on Drug Use and Health, 2004-2013. Treatment rates and payment sources will be compared pre- and post-MHPAEA, testing multiple time-points post-MHPAEA to detect effects of staggered implementation. Survey respondents with private insurance will be compared to those with public sources of insurance and those without insurance. Generalized linear mixed models will be estimated to allow for analysis of individual-level observations clustered within states. The proposed research will produce preliminary empirical evidence on the effectiveness of MHPAEA. Results will be representative at state and national levels. Findings will contribute to an improved understanding of the role health insurance plays in determining how consumers access DAMH care. Findings may also inform future efforts to reduce racial/ethnic disparities in DAMH care and the overall DAMH treatment gap. As other research assesses the effects of the 2010 Affordable Care Act on access to DAMH treatment, the proposed study will provide a strong baseline evidence upon which to build.